The present invention relates to a battery pack having a plurality of electrochemical battery cells, comprising a device for measuring a difference between two cell currents of two different battery cells.
It appears that new battery systems, such as, e.g., lithium-ion batteries, will increasingly be used in the future in stationary applications, such as, e.g., wind turbines and emergency power supplies, as well as in vehicles, such as, e.g., hybrid and electric vehicles. The latter case refers to traction secondary batteries. High demands are placed on such battery systems with regard to effective energy content, charging-discharging efficiency, the absence of a memory effect, service life and reliability.
In order to meet the requirements for a suitable system total voltage, power or energy, battery cells are connected in series or in parallel in such a battery system. The total battery is referred to as the battery pack. Said battery pack is divided into battery cells, battery modules, subunits, a cooling system, a degassing system, sensors and electronic control devices, such as, e.g., the cell supervision circuit (CSC), the battery control unit (BCU), the battery disconnect unit (BDU), current interrupt device (CID) and the battery management system (BMS).
In the case of end-user applications, cylindrical lithium-ion battery cells are primarily used. In the case of high-performance traction secondary batteries, prismatic lithium-ion battery cells in metallic housings consisting of aluminum or stainless steel are preferably used. In this case, there are also embodiments comprising two jelly rolls connected in parallel in a cell housing. A jelly roll is a wound element consisting of an anode layer and a cathode layer.
A battery having jelly rolls connected in parallel is known from the European patent EP232593B1. In this battery, the jelly rolls are oppositely wound and installed in a cell housing. This opposite sense of winding leads to a reduction in the electromagnetic radiation. The principle described in this patent application is also known for traction secondary batteries.
In order to effectively control and monitor lithium-ion batteries, a control of the current via two such jelly rolls is necessary. It is particularly important to detect a difference between two cell currents of two different jelly rolls in order to facilitate a uniform loading of all the cells, or respectively to prevent overloading individual cells.